Data communication protocol in an automatic meter reading system

ABSTRACT

An automatic meter reading (AMR) system includes a fixed or mobile reader and an endpoint. The endpoint is interfaced to a utility meter and the fixed or mobile reader is capable of communicating with the endpoint via RF communication. In this system the fixed or mobile reader sends a message to the endpoint that includes a response mode direction; the response mode direction from the reader tells the endpoint to respond to the reader either in a mobile network mode or a fixed network mode.

CLAIM TO PRIORITY

The present application claims priority to U.S. Provisional PatentApplication No. 60/500,550, (Attorney Docket No. 1725.161US01), filed onSep. 5, 2003, and entitled, “DATA COMMUNICATION PROTOCOL IN AN AUTOMATICMETER READING SYSTEM.”

RELATED APPLICATIONS

This application is related to commonly assigned U.S. ProvisionalApplication No. 60/500,507 (Attorney Docket No. 1725.173US01), filed onSep. 5, 2003, entitled, “SYSTEM AND METHOD FOR DETECTION OF SPECIFICON-AIR DATA RATE,” U.S. Provisional Application No. 60/500,515 (AttorneyDocket No. 1725.162US01), filed Sep. 5, 2003, entitled, “SYSTEM ANDMETHOD FOR MOBILE DEMAND RESET,” U.S. Provisional Application No.60/500,504 (Attorney Docket No. 1725.160US01), filed Sep. 5, 2003,entitled, “SYSTEM AND METHOD FOR OPTIMIZING CONTIGUOUS CHANNEL OPERATIONWITH CELLULAR REUSE,” U.S. Provisional Application No. 60/500,479(Attorney Docket No. 1725.156US01), filed Sep. 5, 2003, entitled,“SYNCHRONOUS DATA RECOVERY SYSTEM,” U.S. Provisional Application No.60/500,550 (Attorney Docket No. 1725.161US01), filed Sep. 5, 2003,entitled, “DATA COMMUNICATION PROTOCOL IN AN AUTOMATIC METER READINGSYSTEM,” U.S. patent application Ser. No. 10/655,760 (Attorney DocketNo. 10145-8011.US00), filed on Sep. 5, 2003, entitled, “SYNCHRONIZINGAND CONTROLLING SOFTWARE DOWNLOADS, SUCH AS FOR COMPONENTS OF A UTILITYMETER-READING SYSTEM,” and U.S. patent application Ser. No. 10/655,759,(Attorney Docket No. 10145-8012.US00) filed on Sep. 5, 2003, entitled,“FIELD DATA COLLECTION AND PROCESSING SYSTEM, SUCH AS FOR ELECTRIC, GAS,AND WATER UTILITY DATA,” which are herein incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to automatic meter reading systems and,more particularly, to the communication protocol used for the endpointto reader hop in the automatic meter reading system.

BACKGROUND OF THE INVENTION

Current automatic meter reading (AMR) systems are significantly limitedin the information that can be obtained from the meter. Generally theAMR system comprises a reader and an endpoint that is interfaced to ameter. In a typical system, the endpoint obtains the consumption readingfrom the meter and then bubbles up every few seconds to send thatconsumption reading, via RF signal, to the reader. Alternatively, theendpoint receives a wake-up tone from the reader that prompts theendpoint to send the consumption reading to the reader.

All that is obtained from this configuration is a single consumptionreading from the meter and that reading is based on what meter registerthe endpoint was programmed with initially at the factory.

As such, there is a need for an AMR system that enables the user of thesystem to have more access to and more control over the information thatthe meter and endpoint can provide.

SUMMARY OF THE INVENTION

The present invention is a data communication protocol used between anendpoint and a reader in an automatic meter reading (AMR) system. Thecommunication protocol enables the reader to have a conversation withthe endpoint in that the reader can tell the meter what to do, it canreconfigure the meter, it can tell the endpoint to reconfigure themeter, it can request a specific response, it can request the endpointto reprogram certain values in both the endpoint and the meter, it canrequest that the end point get specific information from the meter,return it to the end point, which returns it to the reader, etc.

In a preferred embodiment of the present invention, an automatic meterreading (AMR) system includes a fixed or mobile reader and an endpoint.The endpoint is interfaced to a utility meter and the fixed or mobilereader is capable of communicating with the endpoint via RFcommunication. In this system the fixed or mobile reader sends a messageto the endpoint that includes a response mode direction; the responsemode direction from the reader tells the endpoint to respond to thereader either in a mobile network mode or a fixed network mode.

In another embodiment of the invention, the reader uses a single RFcommunication protocol in communicating with the endpoint whetherone-way communication or two-way communication is used. In still anotherembodiment of the invention, the RF communication between the endpointand reader occurs through the use of a communication protocol that usesa data link layer that directs all outbound transmissions from thereader to the endpoint to be either Manchester encoded or transmitted asnon-return to zero data. In still another embodiment of the invention,the communication protocol includes a transport layer that providesslotting control for all data transferred between the reader and theendpoint. In yet another embodiment of the present invention, thecommunication protocol utilizes a command and control frame forcommunication between the reader and endpoint. In still anotherembodiment of the present invention, a plurality of readers andendpoints are provided. The readers are quasi-synchronized in time toprovide a control frame to at least one of the readers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a radio-based automatic meter reading system thatutilizes the data communication protocol of the present invention.

FIG. 2 is a table containing the physical layer specifications of thereader.

FIG. 3A is a table containing the physical layer specifications of theendpoint at data rate 1.

FIG. 3B is a table containing the physical layer specification of theendpoint at data rate 2.

FIG. 4 is a table containing the physical layer specifications of theendpoint in a one-way AMR system.

FIG. 5 is a diagram of a Manchester encoding structure.

FIG. 6 is an example of a Sequence Inversion Keyed Countdown Timer.

FIG. 7 diagrams the data packet structure.

FIG. 8 diagrams a high power pulse data packet structure.

FIG. 9A diagrams a two-way command and control frame.

FIG. 9B diagrams a one-way command and control frame.

FIG. 10 is a table containing universal command types for the datacommunication protocol of the present invention.

FIG. 11 is a table containing type specific commands for the datacommunication protocol of the present invention.

FIG. 12 diagrams command 48 of the data communication protocol, MultipleUngrouped Endpoint Command.

FIG. 13 diagrams command 49 of the data communication protocol, Vectorand Listen Frame.

FIG. 14 diagrams command 50 of the data communication protocol, MultipleCommands to Individual Endpoint.

FIG. 15 is a diagram of the channel spectrum of the system.

FIG. 16 is example of a timing diagram for a staged wakeup sequence fora three cell reuse pattern.

FIG. 17 is an example of a three-cell cellular reuse pattern.

FIG. 18 is an example of a four-cell cellular reuse pattern.

FIG. 19 is an example of a five-cell cellular reuse pattern.

FIG. 20 depicts mobile operation of the system over five channels.

FIG. 21 depicts coverage rings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is a data communication protocol for automaticmeter reading (AMR) systems. The protocol is designed to be flexible andexpandable enabling both one-way and two-way meter reading in both fixedand mobile meter reading systems.

I. System Components

In an AMR system 100, as depicted in FIG. 1, that is utilized with thepresent invention, the components generally include a plurality oftelemetry devices including, but not limited to, electric meters 102,gas meters 104 and water meters 106. Each of the meters may be eitherelectrically or battery powered. The system further includes a pluralityof endpoints 108, wherein each corresponds and interfaces to a meter.Each of the endpoints 108 preferably incorporates a radioreceiver/transmitter, e.g., the Itron, Inc. ERT. The system additionallyincludes one or more readers that may be fixed or mobile, FIG. 1depicts: (1) a mobile hand-held reader 110, such as that used in theItron Off-site meter reading system; (2) a mobile vehicle-equippedreader 112, such as that used in the Itron Mobile AMR system; (3) afixed radio communication network 114, such as the Itron Fixed NetworkAMR system that utilizes the additional components of cell centralcontrol units (CCUs) and network control nodes (NCNs); and (4) a fixedmicro-network system, such as the Itron MicroNetwork AMR system thatutilizes both radio communication through concentrators and telephonecommunications through PSTN. Of course other types of readers may beused without departing from the spirit or scope of the invention.Further included in AMR system 100 is a head-end, host processor 118.The host processor incorporates software that manages the collection ofmetering data and facilitates the transfer of that data to a utility orsupplier billing system 120.

The AMR system 100 and the data protocol is usable in both one-way meterreading and in two-way meter reading. The one-way meter reading systemenables the reader to listen to messages sent asynchronously from theendpoint while the two-way meter reading system enables the reader tocommunicate with and command the endpoint while also enabling theendpoint to respond to the reader.

II. System Protocol

The present communication protocol will be described with reference tothe 1430 MHz band that may be utilized within North America, however, itshould be understood that any other radio frequency band may be used, assuitable, without departing from the spirit or scope of the invention.The present communication protocol will also be described with referenceto the Open Systems Interconnection (OSI) protocol stack of theInternational Standards Organization which includes: (1) the physicallayer; (2) the data link layer; (3) the network layer; (4) the transportlayer; (5) the session layer; (6) the presentation layer; and (7) theapplication layer.

II.A. System Protocol—Physical Layer

The physical layer describes the physical characteristics of thecommunication. This layer conveys the bit stream through the network atthe electrical and mechanical level. It provides the hardware means ofsending and receiving data on a carrier. The physical layerspecifications for the reader may be found in FIG. 2 wherein: (1) theoperational modes; (2) the frequency band; (3) the channel bandwidth;(4) the modulation scheme; (5) the deviation; (6) the encoding; (7) thebit rate; (8) the frequency stability; (9) the minimum receptionsensitivity; (10) the transmission power; (11) the preamble length; and(12) the transmission modes are provided.

The physical layer specification for the endpoint in a two-way AMRsystem, at a first data rate and a second data rate, are found in thetables of FIG. 3A and FIG. 3B, respectively. The specifications providedinclude: (1) the operational modes; (2) the frequency band; (3) thechannel bandwidth; (4) the modulation scheme; (5) the deviation; (6) theencoding; (7) the bit rate; (8) the frequency stability; (9) the minimumreception sensitivity; (10) the minimum preamble length; and (11) thefactory default frequency. The physical layer specification for theendpoint in a one-way AMR system is provided, similarly, in the table ofFIG. 4. However, it should be understood that any other physical layerspecifications may be used, as suitable, without departing from thespirit or scope of the invention.

II.B. System Protocol—Data Link Layer

The data link layer specifies how packets are transported over thephysical layer, including the framing, i.e., the bit patterns that markthe start and end of packets. This layer provides synchronization forthe physical level. It furnishes transmission protocol knowledge andmanagement. In the present data communication protocol, all outbounddata transmissions, i.e., all communications from the reader's centralradio to endpoint, are Manchester encoded with the guaranteed transitionmid-bit and each data bit encoded as a_(n)a_(n)(bar). (See FIG. 5 forthe Manchester Encoding Structure). Inbound transmissions from theendpoint are either transmitted as Manchester encoded data, identical tooutbound transmissions, or are transmitted as NRZ (non-return to zero)data. Selection is based on the value of the MCH flag in the command andcontrol frame.

The data link layer provides a countdown timer. The countdown timer usesSequence Inversion Keying to represent timer bits. Each system isassigned a 10-bit pseudo noise (PN) sequence (for valid sequences, seeTable 1 below). That sequence in the data stream represents a timer bitvalue 0 and the inverse of that sequence in the data stream represents atimer bit value 1. Timer values are composed of 10 timer bits, or 100data bits. The countdown timer begins at 1023 or 1111111111 binary, andcounts sequentially to zero, encoding all timer bits as either thesystem PN sequence or its inverse. The total counter time, in seconds,is 102400/r, where r is the bit rate, in bits per second. FIG. 6provides an example of a Sequence Inversion Keyed Countdown Timer. TABLE1 PN Sequences Sequence Inverted Number Usage Sequence = 0 Sequence = 10 Factory Default 0000000010 1111111101 1 Electric Devices 00000001101111111001 2 Electric Devices 0000001010 1111110101 3 Electric Devices0000001110 1111110001 4 Electric Devices 0000011010 1111100101 5Electric Devices 0000010110 1111101001 6 Electric Devices 00001110101111000101 7 Battery Devices 0000101110 1111010001 8 Battery Devices0001110110 1110001001 9 Battery Devices 0001101110 1110010001 10 BatteryDevices 0000011110 1111100001 11 Battery Devices 0001011110 111010000112 Battery Devices 0001111010 1110000101All inbound packet transmissions are preceded by a 24-bit or 25 bitpreamble and appended with a 16-bit CRC code, which is inclusive of allheader information, but not the preamble, length, or length_bar bytes.The CRC polynomial is 0x1021. The CRC initialization value is 0x0000.CRC processing is performed most significant byte (MSB) first, and thefinal checksum is not inverted.II.C. System Protocol—Network Layer

The network layer specifies how packets get from the source network tothe destination network. This layer handles the routing of the data(sending it in the right direction to the right destination on outgoingtransmissions and receiving incoming transmissions at the packet level).The network layer does routing and forwarding. In the present datacommunication protocol, the network layer functionality is onlyimplemented in electric endpoints, i.e., it is not used forbattery-powered endpoints, or in any endpoint that acts as translator orrepeater. This layer controls the hopping functions that need to occurbetween a reader and any endpoint in order to transfer data. Thishopping protocol is currently used within the Itron AMR systems and istherefore not described in detail herein.

II.D. System Protocol—Transport Layer

The transport layer is used to solve problems like reliability (“did thedata reach the destination?”) and ensure that data arrives in thecorrect order. This layer manages the end-to-end control (for example,determining whether all packets have arrived) and error-checking. Itensures complete data transfer. In the present data communicationprotocol, slotting control is handled in the transport layer. Thisincludes slot assignments, timing, and any necessary packetization. FIG.7 details the packet structure. The message, message type, and flags arereceived from the presentation layer, and broken into appropriatelysized packets. Each packet is prefaced with the endpoint ID, flags,message type, endpoint type, and packet length. The packet lengthreflects the number of bytes in the message itself, exclusive of headerinformation. In the case where more than 254 bytes are required in apacket, the value of the length field is set to 0XFF, and the actuallength of the message structure is placed in bytes 14 (high byte) and 15(low byte), with the message bytes to follow. All packets must have awhole number of bytes in the message.

The packet number byte, when used as part of the message, is configuredas below in Table 2, wherein the first four bits comprise the totalnumber of packets in this message and the last four bits comprise thepacket number. TABLE 2 Packet Number T T T T N N N N MSB LSB

The flags byte is configured as below in Table 3. The first two bits arereserved while the second two bits provides the encoder number (formulti-encoder units), wherein 00=encoder 0, 01=encoder 1, 10=encoder 2,and 11=encoder 3. The fifth bit signifies the status of a pending event,wherein 0=no pending event and 1=a pending event. The sixth bitcomprises the security bit, wherein 0=security disabled and 1=securityenable. The seventh bit comprises the relay bit, wherein 0=message fromoriginating endpoint and 1=message via relay. The eighth bit comprisesthe resend bit, wherein 0=first attempt at packet transmission and1=resend attempt. TABLE 3 Flags R R ENC ENC EVT SEC RLY RSD MSB LSB

Some endpoints in the system have the option of sending out aninfrequent (several times a day) fixed format message at a higher powerlevel, for use in 1-way fixed network applications. The message has itsown structure, as defined in FIG. 8. The custom packet is then BCH (255,139, 15) encoded, prior to transmission. The encoding polynomial is0x461407132060175561570722730247453567445₈. For multi-encoder endpointsthis packet is generated and sent for each individual encoder. The flagsfor the high power pulse data packet structure are configured as shownin Table 4 below. The first four bits are reserved while the fifth andsixth bits provide the encoder number, wherein 00=encoder 0, 01=encoder1, 10=encoder 2, and 11=encoder 3. The seventh bit comprises the relaybit, wherein 0=message from originating endpoint and 1=message viarelay. The eighth bit comprises the error code indicating that acritical endpoint error has occurred. TABLE 4 Flags R R R R ENC ENC RLYERR MSB LSBThe endpoints may also be set to send out any preprogrammed message typein place of the fixed format message described above.II.E. System Protocol—Session Layer

The session layer sets up, coordinates, and terminates conversations,exchanges, and dialogs between the applications at each end. It dealswith session and connection coordination. In the present datacommunication protocol, the session layer generally comprises thecommand and control frame that is sent from the reader to the endpoint.

II.E.i. System Protocol—Session Layer/Two-Way Command and Control

The command and control frame is used to issue command to two-wayendpoints either individually or in groups. It also serves to realignthe endpoint real-time clock. FIG. 9A diagrams the two-way communicationcommand and control frame. As shown, the command and control frametransmission is preceded by a 24-bit preamble, as indicated by the three“P” fields within the frame. The first 16 bits are preferably analternating pattern, AAAAh, and are used for clock recovery. The last 8bits are used for frame and timing synchronization.

Field “0” of the command and control frame comprises the systemidentification (ID). Each system is issued an 8-bit ID value, which isstored in the endpoint, to distinguish different systems withingeographic proximity. The endpoints are designed to respond to commandsfrom their own system or to commands that address them specifically byID number, proper security password, and have a 0x00 in field “0”. Thesystem ID functions nearly identically to the cell ID, described below.However, the system ID is universal, while the cell ID is local, i.e., asingle system will have multiple cells each having the same system IDbut a different cell ID.

Field “1” of the command control frame comprises the frame ID. Eachreader within the system is assigned a frame ID to use based on itsposition in the wake-up sequence. The position in the wakeup sequence isdirectly related to the frequency reuse pattern that is used in a givensystem. Table 1, described earlier, correlates the frame ID to thechannel, which is correlated to the cell reuse ratio.

Field “2” of the command and control frame comprises the cell ID. Eachcell is issued an 8-bit ID value, which is stored in the endpoint, todistinguish different systems within geographic proximity.

Fields “3” through “6” of the command and control frame is the RTC,which is defined as UTC time (coordinated universal time), which is a32-bit value representing the number of seconds since midnight(00:00:00) on Jan. 1, 1970 GMT.

Field “7” is the command flags 1 field, wherein the first three bitsdefine a slot length according to Table 5. TABLE 5 Slot Lengths NominalValue of Length Bits Length in Ticks* Nominal Length in ms 000 81924.99390 001 1638 49.98779 010 3277 100.00610 011 6553 199.98169 1009830 299.98780 101 16384 500.00000 110 32768 1000.00000 111 1638405000.00000*Defined as ticks of an ideal 32,768 Hz clock.The fourth bit is the forward error correction bit, wherein 0=no forwardcorrection error and 1=forward error correct all responses. The fifthbit provides the slot mode, wherein 0=respond to command inpseudo-random slot (Slotted Aloha) and 1=respond to command in thedefined slot. The sixth bit of field “7” defines the data type, wherein0=NRZ response from endpoint and 1=Manchester encoded from the endpoint.The seventh and eighth bits of field “7” comprise the command target,wherein 00=the entire cell, 01=the group defined in EPID_HI (field“12”), 10=the group defined in EPID_LO (field “15”), and 11=the endpointdefined by EPID (including HI/LO), fields “12” through “15”. It shouldbe noted that in single endpoint communications the command target (TGT)is set to 11 and the endpoint responds immediately after commandprocessing with a minimum of 25 milliseconds between this frame and theendpoint response.

Field “8” of the command and control frame is the command flags 2 field,wherein the first four bits are reserved. The fifth and sixth bitsdefined the encoder number, wherein 00=Encoder 0, 01=Encoder 1,10=Encoder 2, and 11=Encoder 3. The final seventh and eighth bits definethe transmit mode, wherein 00=transmit mode 1, e.g., mobile responserequired, 01=transmit mode 2, e.g., fixed network response required, and10/11 are reserved. Also see section V below.

Field “9” of the command and control frame comprises the slot offset.Slot offset defines the number of slots between packets in multi-packetmessages. For example, if the endpoint has an initial slot number of 50,and the slot offset is 120, a three-packet message would be transmittedin slots 50, 170, and 290.

Fields “10” and “11” of the command and control frame define the firstunsolicited message. Specifically, they define the slot number where theunsolicited messages (UMs) are to begin. Any UMs generated during thecell read would be reported in a pseudo-randomly selected slot after theslot defined here. If the value of this field is 0x0000, no UMs are sentfrom the endpoint.

Fields “12” through “15” of the command and control frame provide theendpoint IDs for those endpoints that the reader is desiring tocommunicate with.

Fields “16” and “17” are the security fields and are described furtherin relation to the presentation layer.

Field “18”, defines the command set. The commands are divided into twogroups: (1) universal and (2) type-specific. Universal commands arenumbered 0-63 and are applicable to all the system endpoints. Typespecific commands are numbered 64-255 and vary depending on the lowernibble of the command set field in accordance with Table 6 below. TABLE6 Command Sets Command Set CDS Value Usage  0 (default) 0000 UtilityMetering Endpoints  1 0001 Repeaters and Translators  2 0010 TelemetryDevices  3-14 0011-1110 <<Reserved>> 15 1111 <<Reserved Engineering UseOnly>>

Fields “19” through “21” of the command and control frame define thecommand and command body. Specifically, the eight command bits of field“19” indicate the command type, wherein the numbers 0-63 are universalcommands and 64-255 are the type specific commands. Fields “20” and “21”provide sixteen bits wherein any data needed to carry out the commandtype is provided. The tables in FIGS. 10 and 11 indicate the commandtypes and command bodies that are possible with the system of thepresent invention. Referring to the universal commands (FIG. 10), it canbe seen that the present system is capable of but not limited to: (1)reporting a status; (2) changing a system number to a new system number;(3) changing a group number to a new group number; (4) changing a systemslot number to a new system slot number; (5) changing the cell ID to anew cell ID; (6) reporting slot numbers; (7) resending identifiedpackets of data; (8) setting the receiver bubble-up period; (9) settingthe bubble-up channel; (10) setting the bubble-up time; (11) configuringthe transmission power; (12) setting the channel frequency; etc.

Referring to the type specific commands (FIG. 11), numerous othercommands are available including but not limited to: (1) reportingconsumption data; (2) reporting time of use (TOU) data; (3) reportinglogged data; (4) reporting temperature; (5) reporting tamper data; (6)setting configuration flags; (7) initializing consumption; (8) reportingan event summary; (9) performing an endpoint diagnostic check; (10)reporting memory contents; etc.

Fields “22” and “23” of the command and control frame designate theresponse frequency for the endpoint. The response frequency isconfigured as 16 bit flags, identifying valid response frequencies forthe endpoint. For example, if the response frequency has a value of0x00C1 (bits, 7, 6, and 0 are set), the endpoint may respond on channel,7, channel 6, or channel 0.

Field “24” is reserved for later use.

Field “25” indicates the length of the extended control frame in bytes.A value of 0 indicates that no extended frame is present.

Fields “26” and “27” of the command and control frame provides thecyclic redundancy check (CRC). Specifically, fields “26” and “27”provide a 16-bit CRC. The CRC is preferably a polynomial defined as0x1021. The CRC initialization value is 0x0000. CRC processing isperformed most significant bit (MSB) first, and the final checksum isnot inverted.

II.E.ii. System Protocol—Session Layer/One-Way Command and Control

For simplicity one-way devices may opt to use the programming frameshown in FIG. 9B. The command and command body bytes are similar to thatdescribed above with reference to the two-way devices. The byte fornumber of commands provides the total number of commands to follow inthis frame, with a maximum value of 8. The command flags are diagrammedin Table 7 below. The first two bits indicate the transmit mode, wherein00=transmit mode 0, 01=transmit mode 1, and 10/11 are reserved. Thethird bit designates the data logging, wherein 0=data logging isdisabled and 1=data logging is enabled. The fourth bit designates theforward error correction, wherein 0=disable forward error correction onresponse and 1=enable forward error correction on response. The fifthand sixth bits designate the mode set, wherein 00=stock mode, 01=testmode, 10=reserved mode, and 11=normal mode. The seventh and eighth bitsare reserved. TABLE 7 Command Flags TXM TXM DLG FEC MDE MDE R R MSB LSBII.E.iii. System Protocol—Session Layer/Special Commands—ChannelFrequency

Certain of the commands provided in the command and control frame aredescribed in detail below. For instance, Command 33, which is the setchannel frequency. Each of the system endpoints support up to 16channels, which are set individually. They may or may not be contiguouschannels. The channel numbering differs based on frequency band. Forexample, in the present implementation of the invention, the 1427-1432MHz band is divided into 6.25 kHz frequency channels, with frequencychannel 0 centered at 1427.000 MHz, frequency channel 1 centered at1427.00625 MHz, etc. If endpoint channel 15 is programmed to a value of480, that endpoint receiver will always operate at1427.000+(0.00625*480)=1430.000 MHz. This may be extended to otherfrequency bands. For example, the 433-435 MHz band is divided into 25KHz frequency channels with the frequency channel 0 centered at 433.000MHz, frequency channel 1 centered at 433.025 MHz and so on.

The command body of the set channel frequency command is detailed belowin Table 8: TABLE 8 Command Body/Channel Frequency CHN CHN CHN CHN FRQFRQ FRQ FRQ FRQ FRQ FRQ FRQ FRQ FRQ FRQ FRQ MSB LSB

Individual frequencies are programmed into the endpoint by selecting thechannel being programmed (1-15) with the top nibble, and the frequencynumber in the lower 12 bits. Endpoint channel 0 is preferably themanufacturing default frequency, and may not be edited. Endpoint channel15 is the receiver frequency. It is initialized to the same frequency aschannel 0 at manufacture, and is preferably programmed prior to or atinstallation. The endpoint channel uses are defined in Table 9 below:TABLE 9 Endpoint Channel Use Endpoint Channel Channel Use 0 FactoryDefault. This channel is not reprogrammable. 1 General use Tx/Rx(Transmission/Reception) 2 General use Tx/Rx 3 General use Tx/Rx 4General use Tx/Rx 5 General use Tx/Rx 6 General use Tx/Rx 7 General useTx/Rx 8 General use Tx/Rx 9 General use Tx/Rx 10 General use Tx/Rx 11General use Tx/Rx 12 General use Tx/Rx 13 General use Tx/Rx 14 DefaultUM Channel (unsolicited message) 15 Default Rx Channel

The configuration flag commands, i.e., commands 90, 91, and 92 are usedfor setting individual flags in the endpoints. Each flag commandincludes an 8-bit flag mask and an 8-bit flag as shown below (theconfiguration flags 1 command body): TABLE 10 Flag Mask MSK MSK MSK MSKMSK MSK MSK MSK MSB LSB

TABLE 11 Flags R R R TxB UMC FN FEC MMIThe flag mask field determines which flags are to be modified by thiscommand. A “1” in any bit position means the associated value in theflags field should be modified. For example, A value of 0x17 (bits 4,2,1and 0 are high) means that the values in the Flags field, bits 4, 2, 1,and 0 must be written to the associated flags in the endpoint. Withregard to the flags field of Table 7, the first three bits are reservedfor future growth while the fourth bit, TxB, determines if the endpointis in transmit bubble up mode, the fifth bit, UMC, defines theunsolicited message channel, i.e., UMC=0 then transmit UMs on Channel14, and UMC=1 then transmit UMs on channel 15. The sixth bit of theflags field defines the fixed network mode, wherein 0=this endpointoperates in Mobile/Handheld mode only and 1=this endpoint operates inmobile/handheld/fixed network mode. The seventh bit of the flags fielddefines the forward error correction, wherein 0=no forward errorcorrection applied to the high power pulse and 1=forward errorcorrection is applied to the high power pulse. The eighth bit of theflags field defines the multiple message integration, wherein 0=nomultiple message integration applied to high power pulse and 1=multiplemessage integration applied to high power pulse.II.E.iv. System Protocol—Session Layer/Special Commands—Test Commands

The present data communication protocol provides at least two commandsfor use in system testing and analysis. The first command is command210, i.e., Generate UM (unsolicited message). This command automaticallygenerates an unsolicited message in all endpoints addressed by thecommand and control frame. It generates the lowest numbered UM supportedby the endpoint. The second command is command 211, i.e., EnterScreaming Viking Mode. Screaming Viking Mode is a constant transmissionmode, to be used for test only. When this command is received, theendpoint repetitively transmits its ID for the number of minutesdeclared in the command. If a value of 0 is sent, the mode is active for15 seconds.

II.E.v. System Protocol—Session Layer/Special Commands—ExtensionCommands

Commands 48, 49, 50 and 51 of the data communication protocol areimplemented as extensions to the command and control frame. Theextension commands immediately follow the command and control frame inthe same transmit session. Command 48 is the multiple ungrouped endpointcommand. In the case where the system needs to command a group ofspecific endpoints and vector them to specific slots, command 48 isissued. The central radio then issues commands to these endpoints, asshown in FIG. 12. This command can be used to address a maximum of 16distinct endpoints. The packet length reflects the number of endpointsaddressed by the message. Note that the command 48 may not be used forany command that requires the security password. The structure ofcommand 48 provides for an 8-byte preamble having the value of 0xAAAAAAAA AAAA AA96, the length, the endpoint IDs, and the command bodies foreach of the endpoints and a response byte for each of the endpoints. Theresponse byte is diagrammed in Table 12 below: TABLE 12 Response Byte RR R R CHN CHN CHN CHN MSB LSBThe response byte reserves the first four bits and utilizes the lastfour bits to define the response frequency nibble. Specifically, thefour bit flags define which of the pre-programmed channels the endpointmay respond on. If CHN=0000, then use the response frequency byte fromthe original command and control frame. The structure of the command 48also includes the CRC as described earlier.

Command 49, i.e., the vector and listen frame, is issued in the instancewhere the central radio or reader need to download an arbitrary block ofdata to the endpoint. The endpoint, upon receiving this command receivesa data frame, as defined in FIG. 13. This command is valid only when theendpoints are individually addressed (i.e., TGT=11). The data isendpoint-type specific. Note that the vector and listen frame has an8-byte preamble with a value of 0xAAAA AAAA AAAA AA96. Further, notethat the packet length reflects the number of bytes in the messageitself, exclusive of header information, and that the CRCs computed overall bytes in the message body.

Command 50, the multiple command to individual endpoint command, is usedin the case where the central radio or reader need to download a seriesof commands to one specific endpoint. The endpoint, upon receiving thiscommand, receives a data frame as defined in FIG. 14. This command isonly valid when the endpoints are individually addressed (i.e., TGT=11).Up to 24 commands may be issued to an endpoint using this structure.Note that the packet length reflects the number of commands to be issuedwithin this structure.

Command 51, the Extended Frame Mobile Read command, uses the multipleungrouped endpoint command structure, with a Slotted-ALOHA periodbetween the extended frame and the queried response slots. All endpointswhich recognize the command respond. If the endpoint is among thoseaddressed by the extended frame, it responds as commanded, being offsetby 16 slots. If the endpoint is not specifically addressed it respondsin the Slotted-ALOHA section with its programmed default message.

II.F. System Protocol—Presentation Layer

The presentation layer, which is usually part of an operating system,converts incoming and outgoing data from one presentation format toanother and it is sometimes called the syntax layer. In the present datacommunication protocol, the presentation layer handles data security andany necessary data compression and decompression.

The data security is preferably a simple two-level protocol, which maybe enabled or disabled by the customer. Level 1 provides simpleencryption for the transfer of normal data while level 2 provides writesecurity to the endpoint to prevent unauthorized users from changingendpoint parameters.

Level 1 is intended for use on ordinary data being transmitted from theendpoint to the head end. All data is encrypted with a simple 8-bit XORmask. The level 1 security enables flag and encryption mask and areeditable by a level 2 parameter write. The factory default for the XORmask is the bottom 8 bits of the serial number. Level 1 security isapplied only to the message itself and not to the EPID, flags, ormessage type. Level 1 security may be disabled by setting the mask valueto 0.

Level 2 security is intended for use on any head end commands to changeendpoint parameters. It includes modification of operational, securityand reprogramming parameters. Level 2 functionality is independent andcan be applied with or without Level 1 functions enabled. Each endpointhas a 16-bit password. This password is originally defined at install,and can be edited by a valid Level 2 command. Any write command mustinclude the current password to be considered valid by the endpoint. Foradded security, the Level 1 encryption mask may be applied to thepassword, if Level 1 functionality is active. There is no compressionperformed on packet data.

II.G. System Protocol—Application Layer

The application layer is the layer at which communication partners areidentified, quality of service is identified, user authentication andprivacy are considered, and any constraints on data syntax areidentified. (This layer is not the application itself, although someapplications may perform application layer functions.) In the presentdata communication protocol, an endpoint application layer is used inconjunction with the application programming interface (API). When datais requested by the presentation layer, via the API, the applicationlayer performs its processing and returns the requested message as asingle block, along with one 8-bit value. The value represents themessage type.

III. System Operation

The two-way AMR system of the present invention, at 1430 MHz, isdesigned to operate most efficiently in five contiguous RF channels.This allows the use of a cheaper (wider) receiver section in theendpoint while still maintaining the FCC mandated 50 KHz maximumtransmit spectrum. The transmit spectrum in all devices, endpoints, andreaders, must maintain a 50 KHz or less occupied bandwidth duringtransmit. The receiver in the reader must also have a good selectivityon the channel of interest. The endpoint receiver is allowed to accept awider receive bandwidth primarily to reduce the cost of the endpoint.

Refer to FIG. 15 to observe the 250 KHz of spectrum allocated to thesystem. As shown, the spectrum is divided in to five 50 KHz channels.The center channel, i.e., channel 3, is designated as the controlchannel for the system 100. All endpoints 106 listen on this channel. Assuch, if the readers are quasi-synchronized in their outboundtransmissions the center channel approach allows the endpoints to use awider receive bandwidth while avoiding the interference that wouldnormally be a problem (synchronization is described in further detailbelow). The diagram of FIG. 15, illustrates the bandwidth differencesgraphically. Since the reader has good selectivity the endpoints canrespond on a different channel in each cell simultaneously allowing themaximum data throughput in the system (cell re-use is described infurther detail below).

By utilizing an appropriate RF ASIC, the architecture can be reduced tothree contiguous channels with the reaming two or more channelsscattered throughout the band to ease spectrum allocation requirements.With a reduction in the interference protection to the end point, acompletely separated channel model could be used in an alternativeconfiguration. However, in the separate channel model, the endpointrequires additional base band filtering and is still slightly moresusceptible to adjacent channel interference on the control channelespecially if operating in the high power portion of the band. Theseparate channel option also allows multiple control channels in thesystem when mobile operation is used with multiple outbound channels.When using the separate channel model, channels 2 and 4, of a 5-channelblock, are used for control signals.

To alleviate cell-to-cell interference in a system with a single controlchannel the readers must be synchronized in time so that the controlframes, which are described in further detail below, do not overlap. Theaddition of “dead time” in between sequential control frames allow forthe receivers to be quasi-synchronized instead of in perfect lock step.In the preferred embodiment, quasi-synchronized means that the receiversare within 0.5 seconds of each other, which can easily by achieved viaprotocols such as NTP (network time protocol). Otherquasi-synchronization times may be used without departing from thespirit or scope of the invention. As such, a GPS or other high accuracytime base is not required within the readers.

Within the AMR system, each reader is assigned a frame ID to use basedon its position in a wakeup sequence. The position in the wakeupsequence is directly related to the frequency reuse pattern used in agiven system. The timings in the diagram of FIG. 16 are provided as anexample of a staged wakeup sequence for three cell reuse. As shown, thetimings are for an endpoint to endpoint clock accuracy of +/−0.5seconds, if the value obtainable is only +/−1 second then the dead timemust be increased to 5 and the nominal frame time to 22.5 seconds. Allother timings remain the same. If GPS is available in the reader, thedead time can be reduced and the time frame timing can be shortened. Inany case, the minimum dead time is preferably 0.5 seconds.

As shown in FIG. 16, the first wake-up sequence is initiated at timeT=0. For the first 18.5 seconds, get wakeup (SIK countdown timer), next0.25 seconds (command and control, frame 2), and last 2.5 second is deadtime. The remaining time in the timeline is the hold off time forresponse slots, which is the frame number * the nominal frame time, or2*20=40 seconds of hold off time. At T=20, the second wake-up sequenceis initiated. Similarly, the first 18.5 seconds, get wakeup (SIKcountdown timer), next 0.25 seconds (command and control, frame 1), andthe last 2.5 seconds is dead time. The hold off time for response slotsin this instance is, again, the frame number * the nominal frame time,which is 1*20=20 seconds off hold off time. At T=40, the third wake-upsequence is initiated. For the first 18.5 seconds, get wakeup (SIKcountdown time), the next 0.25 seconds (command and control, frame 0),and the last 2.5 seconds is dead time. The hold off time for response iscalculated as follows, frame number * nominal frame time, or 0*20=0seconds hold off time meaning the endpoints have 2.5 seconds before thebeginning of slot 0 in this cell.

As mentioned, the example of FIG. 16 is for a three cell reuse pattern.However, the example can be easily extended to higher cellular reuseratios by adding more frames as appropriate. In the 1430 MHz system, themaximum recommended cellular reuse is 5. This leads to a hold off timeof 100 seconds in the first cell transmitted which is short enough forthe endpoint to maintain accurate timing with regard to slot timings.

Unless otherwise specified by the system, the frame ID is preferablytied to the cellular frequency used based on Table 13 below: TABLE 13Frame ID Cell Reuse Ratio Channel to Frame ID mapping 3 Cell Channel 1 =Frame ID 0 Channel 3 = Frame ID 1 Channel 5 = Frame ID 2 4 Cell Channel1 = Frame ID 0 Channel 2 = Frame ID 1 Channel 4 = Frame ID 2 Channel 5 =Frame ID 3 5 Cell Channel 1 = Frame ID 0 Channel 2 = Frame ID 1 Channel3 = Frame ID 2 Channel 4 = Frame ID 3 Channel 5 = Frame ID 4To maximize throughput in the system 100, a cellular reuse scheme isemployed in the 1430 MHz band. The reuse ratio is preferably a 3, 4, 5,7, or 9 cell pattern. Smaller patterns are preferred from a delayperspective, however, the final choice is preferably made during the RFplanning and installation of actual systems in the field. The 7 and 9patterns are preferably used in the virtual cell model. The reusepatterns are provided in FIGS. 17, 18, and 19 depicting three-cell(ABC), four-cell (ABCD), and five-cell reuse patterns (ABCDE),respectively.IV. Mobile and Hand-Held Operation

When operating in the mobile or hand-held mode, the 2.5 seconds of “deadtime” does not apply. Rather slot “0” occurs at the end of the commandand control frame plus 25 milliseconds. Note, that due to time requiredto read the attached meter and/or bring the charge pump to fulloperation the endpoint may or may not respond in slot “0” even if toldto respond immediately.

In programming mode, the hand-held control may reduce its sensitivity byas much as 30 dB to avoid overload conditions at close programmingdistances. The hand-held and endpoint must work with programmingdistances as close as 0.5 meters and as far as 300 meters when in themobile mode of operation with a line of site propagation path.

In mobile operation the wake-up sequence, the command & control data,and the receive portions of a standard read cycle are continuouslyrepeated as the mobile moves through the system. The timing ispreferably in the range of a one to five second cycle. The diagramdepicted in FIG. 20 gives a general over view of the mobile operationover the five channels.

The command & control frame preferably contains a group call read thatsolicits a consumptive type reading from all of the endpoints that canhear the mobile and that have the correct system ID. The endpointresponds to the group call in a random slot, on a random channel. Therandom channel is chosen from the list of available channels that isprovided in the command & control frame. The random slot is one of the50 ms slots in the Slotted-ALOHA portion of the frame. (Slotted ALOHA isa random access scheme just like regular ALOHA except that thetransmissions are required to begin and end within the predefinedtimeslot. The timeslots are marked from the end of the command & controlframe just like in the fixed network).

When the reader hears a response from a given endpoint, it knows that itis within range and can request a specific response from the endpoint inthe next command & control frame. The command & control frame isexpected to contain both a standard command frame and an extendedcontrol frame to allow for the mobile to access the most endpointspossible in a single pass. When the mobile requests a response from theend point it will tell it the channel and time slot that it is supposedto respond on. This is to minimize the chances of a collision on thelonger messages that can be delivered in the MDP type of responses.During the mobile cycle, battery endpoints may be required to bubble uptheir receivers up at a higher rate than normal or synchronize to thefirst command & control frame to improve mobile performance.

If the van is moving at a maximum of 30 miles per hour it will travel440 feet in 10 seconds. The van will also have a communications radiusof approximately 500 feet give a 1400 MHz system operating at a datarate of 22.6 Kchips/second, with the expected power levels and receiversensitivities (e.g., +14 dBm endpoint TX power, −110 dBM RX sensitivityin the van, 20 dB margin, endpoint at 5′). The margin is includedbecause the MDP data packet is much longer than the current SCM typemessages and is not repeated unless an error occurs. To achieve a lowre-try rate, it is desirable to bring the BER down to 0.01%. To do thisunder normal situations would require an additional 20 dB of margin,however, a diversity setup on the van receivers can be used to achievethe same results. This requires two antennas on the van placed five tosix feet apart along with an additional receiver demodulator chain perchannel. For SCM data that is repeated multiple times, the system canoperate at a much lower margin and still achieve excellent readreliability in the van. A coverage radius of about 1200 feet is obtainedfor the system when collecting standard consumptive data.

The diagram of FIG. 21, shows the coverage rings for low margin SCMmessages and for the 20 dB margin IDR messages for the present system incomparison with the current 0 dB margin SCM messages from the ERT.

With the current mobile protocol each endpoint is, on average, in therange of the van for approximately 12 to 25 seconds. This is anappropriate amount of time to wake up the endpoint, identify who it is,request an MDP (mobile data packet=250 bytes of raw data maximum) to besent, receive the MDP and potentially retry the request and receiveportions of the process if necessary.

In the basic system, there are five channels at a maximum 75%utilization for MDP responses. This gives an effective data rate of42375 BPS or 5296 bytes per second or 21 blocks per second. Since thesystem is looking at a single block per meter, the system can support 21new meters per second. The mobile then has a nominal range of 500 feet.This gives the system of about 175 meters in range at any given time,even in the densest specified systems. If the van is moving at 30 mph,the system gets 44 feet of new meters per second. In performing ageometric approximation, the result is about 12 new meters per second.So, the system can handle 21 new meters per second but can only get inthe range of 10 to 12 meters per second. This allows for a full set ofretries in a dense system. (This assumes the low 11.36363. KBPS datarate and the full 250 byte MDP, for smaller packets and with the higherdata rate option, the situation is even better.

V. Response Optimization for Mobile and Fixed Network Operation

In order to optimize the batter efficiency, range, and overall systemrobustness for endpoints that must operate in both a mobile and fixednetwork scenario without reprogramming, the following methodology ispreferably used. The outbound transmission from the reader includes aflag that states the response mode of the endpoint. When the responsemode flag is set to “mobile” the endpoint responds at a lower power(e.g., +14 dBm) and in a dynamically randomized slot determined asdescribed above. When the endpoint sees the “fixed network” flag set itresponds in its assigned slot at high power (e.g., +30 dBm). Theadvantage provided by this scenario is that in the mobile case thereader is not burdened with slot dynamic allocation of multiple, whichcan be computationally intensive and consume additional air time tosuccessfully communicate to all the in-range endpoints. It also allowsthe endpoint to conserver power and reduce interference. This leads tothe ability to transmit more data with less retries. In the fixednetwork case, the high power mode enables the system to get maximumrange from the device (reducing infrastructure costs) while interferenceis mitigated by assigned slots. The slots are efficiently assigned inthe fixed network case because of the pseudo-static nature of thesystem. Note that prior art systems enabled only static programming ofthe endpoint to operate in one mode or the other. As such, the previousmethodology did not allow for mixed mode operation without reprogrammingthe endpoint. Thus, the present invention presents the combination oflow power operation and dynamic slot assignment for mobile operationwith the high power slotted operation for the fixed network allcontrolled by a flag in the outbound wakeup data. Refer to field “8,”bits 7 and 8, of the command & control frame that define thetransmit/response mode.

The present invention may be embodied in other specific forms withoutdeparting from the spirit of the essential attributes thereof;therefore, the illustrated embodiment should be considered in allrespects as illustrative and not restrictive, reference being made tothe appended claims rather than to the foregoing description to indicatethe scope of the invention.

1. An automatic meter reading (AMR) system, comprising: a fixed ormobile reader an endpoint interfaced to a utility meter, wherein saidfixed or mobile reader is capable of communicating with said endpointvia RF communication; and wherein said fixed or mobile reader sends amessage to said endpoint that includes a response mode direction forsaid endpoint to respond to said reader in either a mobile or a fixednetwork mode.
 2. The AMR system of claim 1, wherein the mobile responsemode direction directs said endpoint to respond to said reader at a lowpower and in a dynamically randomized slot.
 3. The AMR system of claim1, wherein the fixed network response mode direction directs saidendpoint to respond to said reader at a high power and in an assignedslot.
 4. The AMR system of claim 2, wherein the fixed network responsemode direction directs said endpoint to respond to said reader at a highpower and in an assigned slot.
 5. An automatic meter reading (AMR)system, comprising: a reader; an endpoint interfaced to a utility meter,wherein said reader is capable of communicating with said endpoint viaRF communication; and wherein said reader uses a single RF communicationprotocol in communicating with said endpoint via one-way communicationor two-way communication.
 6. The AMR system of claim 5, wherein one-waycommunication enables said endpoint to communicate with said reader anddeliver a specified message type.
 7. The AMR system of claim 5, whereintwo-way communication enables said reader to communicate with saidendpoint, command said endpoint, and enable said endpoint to respond tosaid reader.
 8. The AMR system of claim 6, wherein two-way communicationenables said reader to communicate with said endpoint, command saidendpoint, and enable said endpoint to respond to said reader.
 9. Anautomatic meter reading (AMR) system, comprising a reader; an endpointinterfaced to a utility meter, wherein said reader is capable ofcommunicating with said endpoint via RF communication; wherein said RFcommunication occurs through the use of a communication protocol, andwherein said communication protocol includes a data link layer directingall outbound data transmissions from said reader to said endpoint to beManchester encoded and directing all inbound transmissions from saidendpoint to said reader to be either Manchester encoded or transmittedas non-return to zero data.
 10. The AMR system of claim 9, wherein saiddata link layer provides a sequence inversion keyed (SIK) countdowntimer.
 11. An automatic meter reading (AMR) system, comprising a reader;an endpoint interfaced to a utility meter, wherein said reader iscapable of communicating with said endpoint via RF communication;wherein said RF communication occurs through the use of a communicationprotocol, and wherein said communication protocol includes a transportlayer, wherein said transport layer provides a slotting control for alldata transferred between said reader and endpoint.
 12. The AMR system ofclaim 11, wherein said slotting control includes slot assignments,timing, and packetization of said data.
 13. The AMR system of claim 12,wherein a packet of packetized data includes a packet number, an ID, aflag, a message type, a message, and an endpoint type.
 14. An automaticmeter reading (AMR) system, comprising a reader; an endpoint interfacedto a utility meter, wherein said reader is capable of communicating withsaid endpoint via RF communication; wherein said RF communication occursthrough the use of a communication protocol, and wherein saidcommunication protocol includes a command and control frame.
 15. The AMRsystem of claim 14, wherein command and control frame issues commands tosaid endpoint.
 16. The AMR system of claim 14, wherein said command andcontrol frame issues realigns a real-time clock within said endpoint.17. The AMR system of claim 14, wherein said command and control frameincludes a command set field.
 18. The AMR system of claim 15, whereinsaid command set includes universal commands and type specific commands.19. The AMR system of claim 14, wherein said command and control frameincludes a command body, wherein said command body provides a commandselected from a group consisting of: reporting a status of saidendpoint; changing a system number of said endpoint; changing a groupnumber of said endpoint; changing a system slot number of said endpoint;changing a cell ID of said endpoint; providing a reporting slot numberto said endpoint; requesting resending of identified packets of datafrom said endpoint; setting a bubble-up channel of said endpoint;configuration a transmission power of said endpoint; or setting achannel frequency of said endpoint.
 20. The AMR system of claim 14,wherein said command and control frame includes a command body, whereinsaid command body provides a command selected from a group consistingof: requesting a report of consumption data from said endpoint;requesting a report of time of use data from said endpoint; requesting areport of logged data from said endpoint; requesting a report of tamperdata from said endpoint; setting a configuration flag within saidendpoint; initializing consumption within said endpoint; request areport of an event summary from said endpoint; performing an endpointdiagnostic check; and requesting a report of memory content of saidendpoint.
 21. The AMR system of claim 14, wherein said command andcontrol frame includes a plurality of fields, and wherein said pluralityof fields are selected from: a frame ID field, a cell ID, a real-timeclock field, a command flag field, a slot offset field, an unsolicitedmessage field, an endpoint ID field, a security field, a command setfield, a command body field, or a response frequency field.
 22. The AMRsystem of claim 14, wherein said command and control frame designates aresponse frequency for said endpoint.
 23. The AMR system of claim 14,wherein said command and control frame comprises a one-way programmingframe or a two-way command and control frame.
 24. The AMR system ofclaim 14, wherein said command and control frame provides a test commandto said endpoint.
 25. An automatic meter reading (AMR) system,comprising: a plurality of readers a plurality of endpoints, whereineach endpoint is interfaced to a utility meter, wherein said pluralityof readers are capable of communicating with said plurality of endpointsvia RF communication; and wherein said plurality of readers arequasi-synchronized in time to provide a control frame to at least one ofsaid plurality of endpoints.